1. Field of the Invention
The present invention relates generally to multiple-conductor flat cables.
2. Description of the Related Art
Electromagnetic wave noise (ElectroMagnetic Interference (EMI)) from electronic equipment such as a personal computer device can adversely affect other electronic equipment. Accordingly, the Voluntary Control council for Interference by Information Technology Equipment (VCCI) requires that each VCCI member be obliged to assure that the strength of the disturbance from his products is contained below VCCI specified level.
When a high-frequency digital signal is fed to an electronic circuit, which is an EMI source, EMI is radiated from a cable that connects circuit boards where the electronic circuit is provided because the cable serves as an antenna where the EMI originates. A measure for suppressing EMI on the electronic circuit can be implemented relatively easily because of technical progress in simulation technology. However, a level of EMI radiated from the cable varies greatly depending on a position and an arrangement of the cable on a real apparatus. For this reason, it is difficult to predict the level of EMI from the cable using simulation technology. Under the circumstances, currently, a measure for suppressing EMI from a cable is applied at a stage of mounting the cable on a real apparatus.
Meanwhile, a technique for suppressing EMI radiation by arranging a flat cable along a conductive member and fixing the conductive member to a casing metal member connected to ground (GND) is disclosed in Japanese Laid-open Patent Application No. 2004-122584.
A technique for suppressing EMI radiation from signal lines by providing a spiral partition wall as a guide and arranging a flat cable along the guide is disclosed in Japanese Patent No. 3849403.
A technique for suppressing EMI radiation by bending or curling a flat cable, rather than linearly arranging the flat cable, thereby avoiding a linear arrangement that increases a radiation noise level in a specific direction is disclosed in Japanese Laid-open Patent Application No. 2003-124596.
However, the technique disclosed in Japanese Laid-open Patent Application No. 2004-122584 is disadvantageous in that the need of arranging the flat cable along the casing metal member connected to GND imposes a limitation on a pathway of the flat cable. Furthermore, in the technique disclosed in Japanese Laid-open Patent Application No. 2004-122584, one unit is made up of a single flat cable and a single conductive member. Accordingly, when applied to electronic equipment having a plurality of flat cables, this technique is disadvantageous in that a limitation is imposed on the implementation space in the electronic equipment.
The technique disclosed in Japanese Patent No. 3849403 is disadvantageous in that addition of the partition wall guide increases cost. The technique disclosed in Japanese Laid-open Patent Application No. 2003-124596 is disadvantageous in that bending or curling the flat cable increases the length of the cable, leading to an increase in impedance.
There is a need to provide a multiple-conductor flat cable that effectively suppresses EMI.